/*
 
(c) 2008 by Sławek Kruczek
slav.mir@gmail.com
 

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.

*/


package analytics.util;


public class RPNOperator implements RPNElement {
    
  
    public enum Type {
        ADD { double eval(double a, double b) { return a + b; } },
        SUB { double eval(double a, double b) { return a - b; } },
        MUL { double eval(double a, double b) { return a * b; } },
        DIV { double eval(double a, double b) { return a / b; } },
        POW { double eval(double a, double b) { return Math.pow(a, b); } };
        
        abstract double eval(double a, double b);
    }
    
    private final Type type;
    
    
    public static RPNOperator parseOperator(String name) {
        switch(name.charAt(0)) {
            case '+': return new RPNOperator(Type.ADD);
            case '-': return new RPNOperator(Type.SUB);
            case '*': return new RPNOperator(Type.MUL);
            case '/': return new RPNOperator(Type.DIV);
            case '^': return new RPNOperator(Type.POW);
            
            default: return null;
        }
    }
    
    
    public RPNOperator(final Type type) {
        this.type = type;
    }

    public Type getType() {
        return type;
    }

    public void exec(RPNExecutionEnvironment env) {
        double b = env.pop();
        env.push(type.eval(env.pop(), b));
    }
}
